Field of the Invention
The present invention relates to an insulating wire and, more particularly, to an insulating wire having partial discharge resistance that exhibits excellent partial discharge resistance and high partial discharge inception voltage and also excellences in the adhesion between the conductor and the insulation layer and the flexibility of the insulation layer, which insulating wire can be prepared by a simple process at a low production cost.
Background Art
The insulating wire refers to a coated insulating wire such as enameled wires used in the form of a coil for electronic devices, including motors, transformers, etc. When the insulating wire applied to a high-voltage motor has low partial discharge inception voltage and poor partial discharge resistance, the localized electric field is concentrated at the tiny gaps between the insulation layers or inside the insulation layer. This can result in partial discharge of electrical energy called corona, ending up a breakdown of the insulation layer.
The charged particles generated as a result of the partial discharge conflict with one another to generate heat and damage the insulation layer to break down, causing insulation breakdown. With a recent trend of using the systems with inverter-driven motors for the purpose of energy conservation, there are a growing number of cases a breakdown of insulation takes place due to the inverter serge in the systems using inverter-driven motors. It has proved that such a breakdown of insulation associated with the inverter serge comes down to the partial discharge which is caused by the overvoltage with the inverter serge.
Korean Patent Open-Laid Publication Nos. 2010-0121513, 2008-0072691 and 2006-0018347 and Japanese Patent Open-Laid Publication Nos. 2004-010714 and 2003-160728 disclose insulating wires using inorganic nanoparticles excellent in partial discharge resistance, such as silica, alumina, titanium oxide, etc., in an insulation coating resin constituting an insulation layer in order to provide the insulating wires with partial discharge resistance. The inorganic nanoparticles not only provide the insulating wires with partial discharge resistance but also contribute to promotion of heat conductivity and strengths and reduction of thermal expansion.
FIG. 1 is a schematic cross-sectional view showing the structure of a conventional insulating wire having an insulation layer containing inorganic nanoparticles. The conventional insulating wire includes, as shown in FIG. 1, a conductor 1 made of a conductive material, such as aluminum, copper, etc., and an insulation layer 2 made of an insulation coating resin disposed to cover around the conductor 1 and containing inorganic nanoparticles 3 having partial discharge resistance.
With an increase in the content of the inorganic nanoparticles 3 in the insulation layer 2, the insulating wire enhances in the partial discharge resistance but undesirably deteriorates in regards to the adhesion between the conductor 1 and the insulation layer 2 and the flexibility of the insulation layer 2. Accordingly, when a wire having a high content of the inorganic nanoparticles 3 in the insulation layer 2 is applied to the coil for electrical devices, a number of cracks occur in the insulation layer 2, resulting in failure to acquire the partial discharge resistance which is the genuine object of the wire.
The insulating wire having the insulation layer 2 containing the inorganic nanoparticles 3 has an effect to suppress a breakdown of insulation caused by the existing partial discharge but cannot prevent the occurrence of the partial discharge fundamentally.
On the other hand, Japanese Patent Laid-Open Publication Nos. 2009-212034 and 2012-119117 and United State patent Laid-Open Publication Nos. 2009-0226720 and 2009-0030134 describe insulating wires that include an insulation layer containing hollow or porous inorganic nanoparticles to secure a low dielectric constant of the insulation layer and thus increase the partial discharge inception voltage, thereby preventing occurrence of the partial discharge.
However, the hollow inorganic nanoparticles which are hollow nano-sized silica are prepared by a complicated preparation process of hollow nanoparticles with a rise of the production cost and also have the difficulty of acquiring a sufficiently low dielectric constant and a high partial discharge inception voltage.
Accordingly, there is a demand for an insulating wire having partial discharge resistance and high partial discharge inception voltage that exhibits excellences in the adhesion between the conductor and the insulation layer and the flexibility of the insulation layer, involves a simple preparation process and a low production cost, and has partial discharge resistance and high partial discharge inception voltage.